So the thing with Debian and any Debian based distro like Ubuntu or Linux Mint is there is no big centralized software repo like the AUR.

The platform for this would be available (https://mpr.makedeb.org).

Yes there is the apt repository but if you want something that’s not in there, get ready to read the documentation or follow random guides.

Not everything is available in the AUR either. It may therefore be necessary to create a own PKGBUILD file. And since anyone can publish something in the AUR, you should check the PKGBUILD file before installing or updating it. Both also require reading guides (https://wiki.archlinux.org/title/Arch_User_Repository, https://wiki.archlinux.org/title/PKGBUILD and so on).

On Arch, all I have to do is Paru -S Reaper,

This would give me the error message that the command was not found. Why do some people assume that everyone uses the same AUR helper as they do? I use aurutils, for example. This AUR helper offers more options but is more cumbersome to use in some cases.

Apart from that, the name of the package is reaper and not Reaper. So even if I would use paru, it would not work.

Now that Arch is so easy to install with the Archscript,

Easier? Yes. But archinstall had and still has some bugs. And archinstall, understandably, does not cover everything so that a manual installation is more flexible.

yeah yeah there’s flathub and stuff but that’s more of a last resort, optimally, you want to get it the correct way.

Appimages or flatpaks are often the correct way to go, as many projects only publish such packages.